Amazon (NASDAQ: AMZN) changed the e-commerce game when it quietly let it be known that it planned to turn its two-day free shipping perk for Prime members into a one-day free shipping perk. That shift, in some ways, took rivals including Walmart(NYSE: WMT) and Target (NYSE: TGT) from being on roughly the same playing field as the online retail giant to being a big step behind.

The question for those major competitors is, should they try to offer one-day shipping on most products as well? That will likely prove a major logistical challenge, given that both companies struggled to match Amazon's two-day standard. It could be argued that it would make more sense for the chains to lean into their brick-and-mortar footprints and leverage the advantages of having a physical presence, rather than trying to keep up with Amazon on its virtual home turf.

Walmart has certainly been working toward that strategy with its omnichannel transformation, but the company has also made it clear that it takes Amazon's plan as a challenge. Walmart management hasn't offered any specific or firm plans in response yet, but the company did provide a clue about its thinking in a bold Tweet.

One-day free shipping...without a membership fee. Now THAT would be groundbreaking. Stay tuned.